234 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On the Density and Composition of Liquid Air. — Experi- 

 ments have been made by Ladenbukg and Krugel on the density 

 of liquid air of varying composition. The method employed was 

 to weigh a glass rod, whose density at 4° was known, in the 

 liquid air contained in a silvered Dewar bulb, by means of a 

 Mohr balance, and to calculate the density from the loss in 

 weight. At the same time, the composition of the air was deter- 

 mined by Bunsen's method, suitably modified for the purpose. 

 In this way three estimations were made. In the first, the 

 liquid air used was freshly prepared ; in the second it had been 

 allowed to stand some time until a portion of the nitrogen had 

 volatilized ; while in the third, it was not used until the second or 

 third day after its preparation. The density of sample one was 

 found to be 0*9951, and its content of oxygen 53*83 percent; 

 that of sample two was 1*029, and its oxygen 64*2 per cent; 

 that of sample three was 1*112 and its oxygen 93*6 per cent. 

 Three facts appear here for the first time : first, that liquid air is 

 lighter than water; second, that the liquid air poorest in oxygen 

 contains over 50 per cent of this element ; and third, that the 

 last portions, consisting of nearly pure oxygen, have a density 

 greater than that of liquid oxygen itself. Moreover the density 

 of the gas from this residue was found to be greater than that of 

 gaseous oxygen; it being 1*125 while that of pure oxygen is 

 1*1056. This is due probably to an admixture either of carbon 

 dioxide or possibly of krypton. From these data the density of 

 ordinary atmospheric air containing 20 per cent of oxygen, and 

 which is not yet obtainable in the liquid state as such, should be 

 calculable, either by geometric or algebraic methods. If the con- 

 tent of oxygen be plotted as abscissas and the density as ordi- 

 nates, three points are obtained lying nearly in a straight line. 

 Prolonging the line connecting either two of these points till it 

 cuts the ordinate drawn through 20 '9 per cent oxygen, values for 

 the density are obtained lying between 0*887 and 6*908. For air 

 free from oxygen, i. e., for pure nitrogen, a value of about 0*84 is 

 obtained, Olszewski having obtained 0*85. Or analytically, as- 

 suming that the three points lie on a curve of the second degree 

 such as y = a + bx + ex 2 , the constants a, b and c can be calcu- 

 lated from the experimental values of y the density, and x the 

 oxygen-content, above given. So that the equation becomes 



y = 0*77892 + 0*00463sc — 0*0000115a; 8 . 

 For the value x = 20*9 per cent of oxygen, this equation gives as 

 the value of y, the density, 0*8707. Hence were it possible to 

 liquefy atmospheric air without the more rapid evaporation of the 

 nitrogen, it would have a density between 0*87 and 0*90. The 

 authors have applied the same method to the determination of the 



